Composite base material

ABSTRACT

There is provided a composite base material, including: carbon fibers having an average fiber length of 3 mm or more and 100 mm or less; and a thermoplastic resin is firmly fixed to the carbon fibers in an amount of 3 to 100 parts by mass with respect to 100 parts by mass of the carbon fibers, wherein a void ratio is more than 7 vol % to less than 100 vol %.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. National Phase Application under 35 U.S.C. §371 ofInternational Application No. PCT/JP2013/068572, filed Jul. 2, 2013, andpublished Under PCT Article 21(2), which claims priority to JapaneseApplication No. 2012-151470, filed Jul. 5, 2012, the entire contents ofeach of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a composite base material that is anintermediate of a carbon fiber-reinforced composite material whichincludes a thermoplastic resin as a matrix, the carbon fiber-reinforcedcomposite material indicating here a precursor directly used formolding, and provides a composite base material excellent in thehandleability and in-plane isotropy and suitable for the production of acarbon fiber-reinforced composite material not including a specificorientation in the in-plane directions and being excellent in thein-plane isotropy and mechanical characteristics.

BACKGROUND ART

In the application where a metal material has been conventionally used,it is an important technical challenge to achieve weight reduction whilemaintaining the mechanical property and productivity required in theapplication by using, instead of a metal material, a fiber-reinforcedcomposite material, particularly a fiber-reinforced composite materialincluding a resin and reinforcing fibers such as a carbon fiber, anaramid fiber or a glass fiber.

For enhancing the mechanical property of the fiber-reinforced compositematerial, a technique of using a continuous fiber or increasing thefiber volume content ratio (VD is known. In the case of using thecontinuous fiber in the fiber-reinforced composite material, themechanical property may be enhanced due to increase of Vf. However, awoven fabric, a unidirectional material, and the like, in which acontinuous fiber is used, generally have a problem that fibers arestacked at various angles, for example, at 0°/+45°/−45°/90°, because ofthe anisotropy of the fibers, and furthermore the stacking processbecomes complicated, for example, the fibers are stacked in planesymmetry, so as to prevent warpage of the shaped product, which leads tolow productivity. On the other hand, in the case of a fiber-reinforcedcomposite material obtained from a mat-form material of cut fibers, itis difficult to enhance the fiber volume content on account of thepresence of fibers in the three-dimensional direction or many fiberentanglements, and the like. In addition, when the mat-form material ofcut fibers is used as a reinforcing fiber of a fiber-reinforcedcomposite material, there is a problem that the reinforcing fiber isdifficult to sufficiently develop strength enhancement due todiscontinuity of the fibers compared with the case of using a continuousfiber, and development rate of strength of the reinforcing fiber in ashaped article is 50% or less relative to the theoretical value. Forexample, Non-Patent Document 1 describes a fiber-reinforced compositematerial obtained from a carbon fiber mat by using a thermosetting resinas a matrix, but development rate of strength of such a fiber-reinforcedcomposite material is about 44% relative to the theoretical value.

A fiber-reinforced composite material including a thermosetting resin asa matrix, which has been conventionally proposed, is obtained bysubjecting an intermediate base material called a prepreg in which areinforcing fiber base material is previously impregnated with athermosetting resin to heating and pressurization by the use of anautoclave, for 2 hours or more depending on the case. In recent years,there has been proposed an RTM method where a reinforcing fiber basematerial not impregnated with a resin is set in a mold and then athermosetting resin is infused therein, and the molding time has beengreatly shortened. However, even when the RTM method is used, molding ofone component requires 10 minutes or more (Patent Document 1).

Accordingly, attention has been focused on a composite materialincluding, as a matrix, a thermoplastic resin in place of theconventional thermosetting resin, particularly, on a composite materialincluding a carbon fiber as a reinforcing fiber (carbon fiber-reinforcedcomposite material). However, the thermoplastic resin requires a longtime to impregnate a fiber base material with the resin because of highviscosity compared with a thermosetting resin, as a result, the tacttime for molding disadvantageously becomes long. In addition, it isknown that a carbon fiber-reinforced composite material having anin-plane isotropy, in which carbon fibers are not oriented in a specificdirection in the plane, is preferred, but when forming a compositematerial by impregnating a carbon fiber mat, or the like, with athermoplastic resin, a high pressure is required for the impregnationdue to high viscosity of the thermoplastic resin in a molten state, andthere is a problem that it becomes difficult to maintain the in-planeisotropy by generating disorder of fiber orientation attributed to flowof the fibers and resin as in the molding.

CITATION LIST Patent Document

Patent Document 1: JP-A-2008-68720 (the term “JP-A” as used herein meansan “unexamined published Japanese patent application”)

Non-Patent Document

Non-Patent Document 1: Composite Part A, 38 (2007), pp. 755-770

SUMMARY OF INVENTION Problems that Invention is to Solve

An object of the present invention is to provide a composite basematerial excellent in the handleability and in-plane isotropy andsuitable for the production of a carbon fiber-reinforced compositematerial and not including a specific orientation in the in-planedirections and being excellent in the in-plane isotropy and mechanicalcharacteristics.

Means for Solving Problems

As a result of intensive studies to solve the above-described problems,the present inventors have focused attention on an intermediate at aprevious stage of a precursor (fiber-reinforced composite material)which is a molding material directly used for molding and found that acomposite base material constituted by a carbon fiber and athermoplastic resin and having a specific void ratio is suitable as theintermediate of the carbon fiber-reinforced composite material. Thepresent invention has been accomplished based on this finding. Theconfigurations of the present invention are set forth below.

[1] A composite base material, including: carbon fibers having anaverage fiber length of 3 mm or more and 100 mm or less; and athermoplastic resin is firmly fixed to the carbon fibers in an amount of3 to 1000 parts by mass with respect to 100 parts by mass of the carbonfibers, wherein a void ratio of the composite base material is more than7 vol % to less than 100 vol %.

[2] The composite base material according to [1], wherein the compositebase material is obtained by heating and pressurizing a mat-formmaterial in which a carbon fiber mat and a thermoplastic resin arecombined, and the composite base material is obtained by applying heatand pressure so that a decrease in the void ratio does not exceed 40 vol% in one heating and pressurizing treatment.

[3] The composite base material according to [1] or [2], wherein thecomposite base material is obtained by heating and pressurizing amat-form material in which a carbon fiber mat and a thermoplastic resinare combined, and the composite base material has the void ratio of morethan 7 vol % to less than 80 vol %, obtained by preparing a compositebase material having a void ratio of 60 vol % or more and furtherheating and pressurizing the composite base material so that a decreasein the void ratio does not exceed 20 vol % in one heating andpressurizing treatment.

[4] The composite base material according to any one of [1] to [3],wherein the composite base material is obtained by heating andpressurizing a mat-form material in which a carbon fiber mat and athermoplastic resin are combined, and the composite base material is acomposite base material having a void ratio of from more than 7 vol % toless than 80 vol %, obtained by preparing a composite base materialhaving a void ratio of from 40 vol % to less than 60 vol % and furtherheating and pressurizing the composite base material so that a decreasein the void ratio does not exceed 30 vol % in one heating andpressurizing treatment.

[5] The composite base material according to any one of [1] to [4],wherein a width of the carbon fibers is 5 mm or less and a thickness ofthe carbon fibers is ½ or less of the width.

[6] The composite base material according to any one of [1] to [5],wherein a carbon fiber bundle (A) constituted by the carbon fibers ofnot less than a critical number of single fibers, defined by thefollowing formula (1), is present in the carbon fibers:Critical number of single fibers=600/D  (1)

wherein D is an average fiber diameter (μm) of single carbon fibers.

[7] The composite base material according to [6], wherein a ratio of thecarbon fiber bundle (A) to a total amount of the carbon fibers containedin the composite base material is more than 0 vol % to less than 99 vol%.

[8] The composite base material according to [6] or [7], wherein anaverage number (N) of fibers in the carbon fiber bundle (A) satisfiesthe following formula (2):0.7×10⁴ /D ² <N<2×10⁵ /D ²  (2)

wherein D is the average fiber diameter (μm) of single carbon fibers.

[9] The composite base material according to any one of [1] to [8],wherein the carbon fibers are in a mat-form material in which the carbonfibers are two-dimensionally randomly oriented.

[10] A composite material obtained by pressurizing the composite basematerial according to any one of [1] to [9].

[11] The composite material according to [10], wherein a void ratio ofthe composite material is from 0 to 7 vol %.

Advantageous Effects of Invention

The composite base material of the present invention is suitable as anintermediate of a carbon fiber-reinforced composite material(hereinafter, sometimes simply referred to as a composite material) andexcellent in the handleability and in-plane isotropy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a cutting step.

FIG. 2 is a schematic view showing a front surface and a cross-sectionalsurface in one example of a rotary cutter having a spiral knife.

FIG. 3 is a schematic view showing a front surface and a cross-sectionalsurface in one example of a rotary cutter having a fiber separatingknife.

FIG. 4 is a schematic view showing one example of a fiber separatingcutter having a blade that is parallel to the fiber direction and has aslit function, in addition to a blade perpendicular to the fiberdirection.

FIG. 5 is a schematic view showing one example of theheating/pressurizing step.

DESCRIPTION OF EMBODIMENTS

The embodiments of the present invention are sequentially describedbelow. In the following, as regards the present invention, the term“weight” is used in some places, but the weight always means the mass.

[Composite Base Material]

In the composite base material of the present invention, from 3 to 1,000parts by mass of a thermoplastic resin is firmly fixed to 100 parts bymass of a carbon fiber having an average fiber length of 3 mm or moreand 100 mm or less, and a void ratio of the composite base material isfrom more than 7 vol % to less than 100 vol %.

The void ratio is a ratio of air contained in the composite basematerial of the present invention and is defined based on the followingformula (3) and expressed by the percentage on the volume basis (vol %).Void ratio (Vr)=(t ₂ −t ₁)/t ₂×100  (3)(Here, t₁ is a theoretical thickness when the composite base materialhas a void ratio of 0 vol %, which is calculated from the amounts of thecarbon fiber and thermoplastic resin contained in the composite basematerial, and t₂ is the average thickness of the composite basematerial).

In formula (3), as to t₁ and t₂, a numerical quantity expressed byvarious length units such as millimeter (mm), centimeter (cm) and meter(m) may be employed, but of course, t₁ and t₂ are numerical quantitiesexpressed by the same unit. In addition, t₁ and t₂ are the thicknessesof the composite base material per the same specific area of thecomposite base material.

The void ratio of the composite base material of the present inventionis from more than 7 vol % and less than 100 vol % as described above butis preferably less than 90 vol %, more preferably 80 vol % or less,still more preferably 75 vol % or less, yet still more preferably 50 vol% or less, and even yet still more preferably 40 vol % or less.

Furthermore, the void ratio of the composite base material of thepresent invention is preferably from 10 vol % or more and less than 100vol %, more preferably from 10 vol % or more and less than 90 vol %,still more preferably from 10 vol % or more and 80 vol % or less, yetstill more preferably 20 vol % or more and 75 vol % or less, even yetstill more preferably 25 vol % or more and 50 vol % or less, and aboveall, preferably 30 vol % or more and 40 vol % or less.

In the composite base material of the present invention, a thermoplasticresin is in a state of being firmly fixed to a carbon fiber. The stateof being firmly fixed is obtained, as described later with respect tothe method for producing the composite base material of the presentinvention, by the following processes, or the like. The processesinclude a process of supplying a thermoplastic resin sheet or moltenthermoplastic resin to a mat-form material in which carbon fibers areentangled with each other (hereinafter, sometimes referred to as acarbon fiber mat) and applying heat and pressure to perform impregnationand a process of heating a mixed mat-form material in which athermoplastic resin powder or fiber is attached to or entangled with amat-form material in which carbon fibers are entangled with each other(in the present invention, the mixed mat-form material is referred to asa mixed random mat and hereinafter, except as otherwise noted, a randommat used indicates the mixed mat-form material) at a temperature notless than the softening point (which indicates, in the presentinvention, the melting point of the thermoplastic resin when the resinis crystalline, and indicates the glass transition temperature when theresin is amorphous) of the thermoplastic resin and applying pressure incombination depending on the case. The state of being firmly fixedindicates a state where a thermoplastic resin is caused to reach allparts between fiber bundles as well as inside the fiber bundle in themat-form material of carbon fiber and be integrated with the carbonfiber. In the composite base material of the present invention, whencarbon fiber mats or random mats including carbon fiberstwo-dimensionally randomly oriented, this is very preferred, because thein-plane isotropy of the composite base material is excellent and thecomposite material obtained from the composite base material is alsoexcellent in the in-plane isotropy.

The composite base material of the present invention is not particularlylimited in its shape, but examples thereof include a plate-shapedmaterial having a smaller dimension in the thickness direction than onein the plane direction, in particular a substantially rectangularplate-shaped material, which is representative, and the plate-shapedmaterial may be a so-called long material.

A mat where a solid sheet or sheet-like melt of a thermoplastic resin islayered on a carbon fiber mat is referred to as a layered random mat.

In the present invention, the term “composite random mat” is used as abroader concept encompassing the above-described mixed random mat andlayered random mat and refers to a mat-form material where a carbonfiber mat and a thermoplastic resin are combined by mixing, stacking, orthe like.

[Carbon Fiber]

The carbon fiber constituting the composite base material of the presentinvention is discontinuous and has an average fiber length of 3 mm ormore and 100 mm or less. The composite base material of the presentinvention is characterized by containing a carbon fiber that is long toa certain extent, and thereby being capable of developing a reinforcingfunction, and the average fiber length of carbon fibers is preferablyfrom 5 mm or more and 100 mm or less, more preferably 10 mm or more and100 mm or less, still more preferably 15 mm or more and 80 mm or less,yet still more preferably 20 mm or more and 60 mm or less. Although themethod for producing the composite base material of the presentinvention is described later, when cutting a carbon strand in thecutting step thereof, the strand can be cut into a constant cut length,for example, 50 mm. The average fiber length of the carbon fibers in acomposite base material obtained using the carbon fiber strand aftercutting becomes the cut length above.

In the composite base material of the present invention, the carbonfiber a real weight is preferably from 25 g/m² or more and 10,000 g/m²or less, more preferably 25 g/m² or more and 5,000 g/m² or less, stillmore preferably from 25 g/m² or more and 3,000 g/m² or less.

The average fiber diameter of the carbon fibers contained in thecomposite base material of the present invention is preferably from 3 to12 μm, more preferably from 5 to 9 μm, still more preferably from 5 to 7μm. A carbon fiber adhered to a sizing agent is preferably used. Theamount of the sizing agent adhered is preferably more than 0 parts bymass to 10 parts by mass, per 100 parts by mass of the carbon fiber.

In addition, the carbon fiber contained in the composite base materialof the present invention is preferably a fiber subjected to fiberopening. The fiber opening as defined herein means that, as describedlater by an example regarding the method for producing the compositebase material of the present invention, a carbon fiber strand afteradjusting the bundle of carbon fibers to be wide and thin is, forexample, passed through a fiber separating step, or the like, andthereby adjusted to a certain ratio of the fiber bundle to the amount ofsingle fibers and a certain number of collected fibers in fiber bundles.The composite base material of the present invention is preferably amat-form material in which carbon fibers, that is, carbon fiber bundlesor single carbon fibers, are entangled with each other. In particular, amat-form material in which as seen in the case of spraying anddepositing carbon fiber bundles and the like after cutting the carbonfiber strand into a specific length, the carbon fiber bundles and thelike are deposited while being two-dimensionally entangled with eachother to form a pseudo flat plane and individual carbon fibers areoriented in the pseudo flat plane, that is, carbon fibers or the likeare two-dimensionally randomly oriented, is preferable for the compositebase material of the present invention. This is because thetwo-dimensionally randomly oriented state of carbon fibers or the likein the mat-form material is maintained also in the composite basematerial and from such a composite base material, a composite materialexcellent in the in-plane isotropy and mechanical property can beobtained.

The carbon fiber includes a polyacrylonitrile-based (hereinafter,sometimes simply referred to as PAN-based) carbon fiber, a pitch-basedcarbon fiber, a rayon-based carbon fiber, or the like depending on theprecursor thereof, and all of these types can be used for the compositebase material of the present invention, but among others, a PAN-basedcarbon fiber is preferred in view of physical properties and cost.

In the present invention, the carbon fiber strand is a bundle of longcarbon fibers, where carbon fiber filaments (single fibers) arecollected with the number of single fibers being about 1,000 or more,and indicates a bundle that can be wound onto a bobbin (a cylindricalspool) to be transported or handled and has a length long enough toenable a continuous processing for a given time in the later-describedwidening step or the like.

[Degree of Fiber Opening]

In general, the commercially available carbon fiber is in the form of afiber bundle where from thousands to ten thousands of filaments (singlefibers) are collected. Above all, in the case of obtaining a thin-walledcomposite material, when the carbon fiber in the form of a fiber bundleis used as it is, the entangled portion of fibers becomes locally thickand a thin-walled article cannot be obtained. Therefore, use of a carbonfiber after fiber opening is important, and it is preferred that thecomposite base material of the present invention is formed as acomposite base material having a controlled degree of fiber opening andcontains a carbon fiber bundle constituted by carbon fibers of not lessthan a specific number and another opened carbon fiber in a specificratio.

In the description of the present invention, the term “fiber separating”is also sometimes used below, and the fiber separating indicates that acarbon fiber bundle, particularly, a carbon fiber strand, is separatedinto two or more carbon fiber bundles. When a carbon fiber strand isprocessed by both of the later-described widening and the fiberseparating, an opened carbon fiber (strand) is obtained.

That is, the carbon fiber in the composite base material of the presentinvention is preferably constituted by a carbon fiber bundle (A)constituted by carbon fibers of not less than a critical number ofsingle fibers defined by the following formula (1), and another openedcarbon fiber, i.e., a single fiber or a fiber bundle constituted bycarbon fibers of less than the critical number of single fibers.Critical number of single fibers=600/D  (1)(Here, D is the average fiber diameter (μm) of single carbon fibers.

As for the carbon fiber in the composite base material of the presentinvention, the ratio of the carbon fiber bundle (A) to the total amountof the carbon fibers contained is preferably more than 0 vol % and lessthan 99 vol %. If the ratio of the carbon fiber bundle (A) is 99 vol %or more, the entangled portion of fibers becomes locally thick and athin-walled article may not be obtained. The ratio of the carbon fiberbundle (A) is more preferably from 30 vol % or more and less than 95 vol%, still more preferably 50 vol % or more and less than 90 vol %.

For controlling the content of the carbon fiber bundle to the targetratio, in the later-described preferable production method, the contentcan be controlled, for example, by the pressure of air blown in thefiber opening step or the like. In addition, the content can becontrolled by adjusting the size, for example, the bundle width or thenumber of fibers per width, of the fiber bundle subjected to a cuttingstep. Specifically, the method therefor includes a method of wideningfiber bundle and providing a slit step before the cutting step andfurther includes a method of cutting fiber bundle by using a so-calledfiber separating knife in which many short blades are arranged, and amethod of slitting fiber bundle simultaneously with cutting. Preferablefiber opening conditions are described in the section of the fiberopening step.

Furthermore, in the composite base material of the present invention,the average number (N) of fibers in the carbon fiber bundle (A)preferably satisfies the following formula (2).0.7×10⁴ /D ² <N<2×10⁵ /D ²  (2)(Here, D is the average fiber diameter (μm) of single carbon fibers.

If the average number (N) of fibers in the carbon fiber bundle (A) is0.7×10⁴/D² or less, a high fiber volume content (VD becomes difficult tobe obtained. If the average number (N) of fibers in the carbon fiberbundle (A) is 2×10⁵/D² or more, a thick portion is locally generated totends to cause a void.

For controlling the average number (N) of fibers in the carbon fiberbundle (A) to the target numerical quantity, in the later-describedpreferable production method, the average number can be controlled byadjusting the size, for example, the bundle width or the number offibers per width, of the fiber bundle subjected to a cutting step.Specifically, the method therefor includes a method of widening thefiber and providing a slit step before the cutting step. In addition,the average number (N) of fiber bundles in the carbon fiber bundle (A)can also be controlled by adjusting the degree of fiber opening of thecut fiber bundle, for example, by the pressure of air blown in the fiberopening step. Preferable conditions are described in the paragraphs ofthe cutting step and fiber opening step.

In this way, by using a composite base material including a carbon fiberbundle (A) constituted by carbon fibers of not less than a criticalnumber of single fibers defined by formula (1) and a carbon fiber (B) ina single fiber state or constituted by carbon fibers of less than thecritical number of single fibers at the same time, a composite materialwith good fiber filling efficiency, little scattering in fiber density,and more excellent mechanical strength can be provided.

In addition, a carbon fiber bundle constituted by carbon fibers of notless than a specific number of carbon fibers and another opened carbonfiber are present together in a specific ratio, and whereby the contentof the carbon fiber in the composite base material, i.e., the fibervolume content ratio (Vf) can be increased.

Specifically, in the case where the average fiber diameter of the carbonfibers constituting the composite base material is from 5 to 7 μm, thecritical number of single fibers is from 86 to 120.

In the case where the average fiber diameter of the carbon fiber is 5μm, the average number of fibers in the fiber bundle is from more than280 to less than 8,000, preferably from 600 to 6,000. In the case wherethe average fiber diameter of the carbon fiber is 7 μm, the averagenumber of fibers in the fiber bundle is from more than 142 to less than4,082, preferably from 400 to 4,000. The composite base material of thepresent invention can have various thicknesses and by using such acomposite base material, even a shaped article having a final thicknessof approximately from 0.2 to 4 mm can be obtained.

[Thermoplastic Resin]

In the composite base material of the present invention, a thermoplasticresin is present in the state of being firmly fixed to a carbon fiber,and the content of the thermoplastic resin is from 3 to 1,000 parts bymass per 100 parts by mass of the carbon fiber, preferably from 50 to500 parts by mass per 100 parts by mass of the carbon fiber, still morepreferably from 50 to 300 parts by mass per 100 parts by mass of thecarbon fiber.

A preferable method for producing the composite base material of thepresent invention is described in detail later, but the thermoplasticresin is used in a fiber form, particle form, sheet form in a moltenstate, or in the form of two or more kinds of these states, and afterobtaining a composite random mat, the composite random mat is heated andpressurized, and whereby the thermoplastic resin is melted in thecomposite random mat and impregnates between carbon fibers to produce acomposite base material. In the case where the thermoplastic resin usedis in the particle shape, the average particle diameter is preferablyfrom 0.01 μm to 3 mm, more preferably from 0.1 μm to 1 mm, still morepreferably from 1 μm to 0.8 mm. The particle size distribution of theparticle-shaped thermoplastic resin is not particularly limited, but aresin with a small distribution is more preferred for the purpose ofobtaining a more homogeneous composite base material. Theparticle-shaped thermoplastic resin can be preferably used in thepresent invention as a resin having the objective particle sizedistribution by applying a treatment such as classification. As for thefiber-shaped thermoplastic resin, the fineness is preferably from 100 to5,000 dtex, more preferably from 1,000 to 2,000 dtex. The average fiberlength of the particle-shaped thermoplastic resin is preferably from 0.5to 50 mm, more preferably from 1 to 10 mm. In the case of a sheet-shapedthermoplastic resin, the sheet is disposed on one surface or bothsurfaces of a mat satisfying the above-described embodiments of thecarbon fiber. The thickness of the sheet-shaped thermoplastic resin isappropriately set according to the thickness of the final shaped productand the content of the thermoplastic resin relative to the carbon fiberbut is preferably from 0.1 to 10 mm, more preferably from 0.5 to 4 mm.

The thermoplastic resin is not particularly limited in its kind but, asdescribed above, a resin capable of taking on its shape in fiber,particle or sheet form is preferred, and a resin may be used alone or aplurality of kinds of resins may be used. The thermoplastic resinincludes, for example, vinyl chloride resin, vinylidene chloride resin,vinyl acetate resin, polyvinyl alcohol resin, polystyrene resin,acrylonitrile-styrene resin (AS resin), acrylonitrile-butadiene-styreneresin (ABS resin), acrylic resin, methacrylic resin, polyethylene resin,polypropylene resin, polyamide 4 resin, polyamide 6 resin, polyamide 11resin, polyamide 12 resin, polyamide 26 resin, polyamide 46 resin,polyamide 66 resin, polyamide 69 resin, polyamide 610 resin, polyamide611 resin, polyamide 612 resin, polyamide 1212 resin, polyamide 6Tresin, polyamide 6I resin, polyamide 11 resin, polyamide 912 resin,polyamide 1012 resin, polyamide 9T resin, polyamide 91 resin, polyamide10T resin, polyamide 10I resin, polyamide 11T resin, polyamide 11Iresin, polyamide 12T resin, polyamide 12I resin, polyamide MXD6 resin,polyacetal resin, polycarbonate resin, polyethylene terephthalate resin,polyethylene naphthalate resin, polytrimethylene terephthalate resin,polytrimethylene naphthalate resin, polybutylene naphthalate resin,polybutylene terephthalate resin, poly(1,4-cyclohexanedimethanolterephthalate), polylactic acid resin, polyarylate resin, polyvinylnaphthalate resin, polyphenylene ether resin, polyphenylene sulfideresin, polysulfone resin, polyethersulfone resin, polyether ether ketoneresin, a copolymer or modification product thereof, and a blend orpolymer alloy of two or more kinds of these resins.

Among these thermoplastic resins, preferred are a polyamide resin suchas polyamide 4 resin, polyamide 6 resin, polyamide 11 resin, polyamide12 resin, polyamide 26 resin, polyamide 46 resin, polyamide 66 resin,polyamide 69 resin, polyamide 610 resin, polyamide 611 resin, polyamide612 resin, polyamide 1212 resin, polyamide 6T resin, polyamide 6I resin,polyamide 11 resin, polyamide 912 resin, polyamide 1012 resin, polyamide9T resin, polyamide 9I resin, polyamide 10T resin, polyamide 10I resin,polyamide 11T resin, polyamide 11I resin, polyamide 12T resin, polyamide121 resin and polyamide MXD6 resin, a polyester resin such aspolyethylene terephthalate resin, polyethylene naphthalate resin,polytrimethylene terephthalate resin, polytrimethylene naphthalateresin, polybutylene naphthalate resin, polybutylene terephthalate resin,poly(1,4-cyclohexanedimethanol terephthalate), polylactic acid resin andpolyarylate resin, a polycarbonate resin, a copolymer or modificationproduct thereof, and a blend or polymer alloy of two or more kinds ofthese resins.

[Other Agents]

In the following, the thermoplastic resin contained in the compositebase material of the present invention is sometimes simply referred to amatrix resin.

In the composite base material of the present invention, various fibrousfillers such as an inorganic fiber other than carbon fiber, typified bya glass fiber, a ceramic fiber and a metal fiber, and an organic fibertypified by an aramid fiber, non-fibrous fillers, or various additivessuch as flame retardant, UV-resistant agent, pigment, release agent,softening agent, plasticizer and surfactant, may be incorporated as longas the object of the present invention is not impaired.

[Production Method]

A preferable method for obtaining the composite base material of thepresent invention is described below. For example, the composite basematerial of the present invention may be preferably produced through thefollowing steps 1 to 5:

1. a widening step: a step of widening a carbon fiber strand,

2. a cutting step: a step of cutting the carbon fiber strand,

3. a spraying step: a step of spreading/spraying the widened and cutcarbon fiber strand alone to form a carbon fiber mat, or a step ofspreading/spraying the widened and cut carbon fiber strand together witha fibrous or powdery thermoplastic resin to form a (mixed) random matthat is a mixture thereof,

4. a conveying step: a step of conveying the (mixed) random mat, or astep of conveying the carbon fiber mat and in the course of conveyance,supplying a sheet-shaped molten thermoplastic resin to one surface orboth surfaces of the carbon fiber mat, and

5. a heating/pressurizing step: a step of heating and pressurizing theconveyed (mixed) random mat or the conveyed carbon fiber mat adhered toa sheet-form molten thermoplastic resin (layered random mat), to obtaina composite base material.

[Widening Step]

A strand of a high-function fiber such as carbon fiber exerts furthereffectively its function when widened, i.e., when fiber bundles arewidely and thinly arranged, for example, by applying a physical force.In the production of the composite material of the present invention,the carbon fiber strand is preferably widened. The step of widening thecarbon fiber strand, i.e., making the carbon fiber bundle wide and thin,may be continuous or discontinuous with a step subsequent to this step.

As the method for widening the carbon fiber strand when producing thecomposite base material of the present invention, a known method may beemployed. For example, a plurality of carbon fiber strands drawn outfrom a bobbin are continuously contacted under a specific tension with aplurality of bars that are disposed orthogonally to the runningdirection of the strand and each has a circular cross-sectional profile,and whereby the carbon fiber strand can be widened in multiple stages.The widened width is preferably from 1.1 to 5 times, more preferablyfrom 1.1 to 3 times, relative to the width of the carbon fiber stranddrawn out from the bobbin.

[Cutting Step]

The step of cutting the widened carbon fiber strand is described below.As the method for cutting the carbon fiber strand, a known method may beemployed, but a method using a knife such as rotary cutter is preferred.

The rotary cutter is preferably a cutter provided with a spiral knife atan angle specified or with a so-called fiber separating knife havingarranged therein a plurality of short blades. FIG. 1 shows a specificschematic view of the cutting step. FIG. 2 shows one example of therotary cutter having a spiral knife, and FIG. 3 shows one example of therotary cutter having a fiber separating knife.

The average number (N) of fibers in the carbon fiber bundle (A) ispreferably controlled by adjusting the size, for example, the bundlewidth or the number of fibers per width, of the fiber bundle subjectedto the cutting step so as to fall in the preferred range of the presentinvention.

As the fiber bundle strand for cutting, a strand previously having anumber of fiber bundles in the range of formula (2) is preferably used.However, in general, as the number of fiber bundles is smaller, the costof the carbon fiber is higher. Therefore, in the case of using aninexpensively available carbon fiber strand having a large number offiber bundles, the carbon fiber strand for use in the cutting step ispreferably subjected to the cutting step after adjusting the width orthe number of fibers per width. Specifically, the method thereforincludes a method where the carbon fiber strand is widened in the widthand thereby thinned through the widening step above and then subjectedto the cutting step, and a method where the carbon fiber strand issubjected to the cutting step through slitting process after thewidening step. In the method of carrying out slitting process, thecarbon fiber strand is subjected to the cutting step after previouslyadjusting the number of fiber bundles to the range of formula (2) andtherefore, an ordinary blade having no special mechanism, such as flatblade and spiral blade, can be used as the cutter.

In addition, there is a method of cutting the fiber bundle by using afiber separating knife, and a method of slitting the fiber bundlesimultaneously with cutting by using a cutter having a slit function.

In the case of using a fiber separating knife, the average number (N) offibers can be decreased by using a knife with a narrow width, or on thecontrary, the average number (N) of fibers can be increased by using aknife with a wide width.

As for the cutter having a slit function, FIG. 4 shows an example of afiber separating cutter having a blade that is parallel to the fiberdirection and has a slit function, in addition to a blade perpendicularto the fiber direction. In this fiber separating cutter, short bladesperpendicular to the fiber direction are spirally provided at a certaininterval, and the fiber can be cut by these blades and concurrently slitby the blade perpendicular to the fiber direction. In the fiberseparating cutter shown in FIG. 4, as illustrated in the figure, theangle θ between the circumferential direction of the rotary cutter andthe arranging direction of the knife is also constant.

For stably developing mechanical characteristics of the finally obtainedcomposite material and obtaining a composite material excellent in thesurface appearance, the unevenness in fiber density has a great effect.In a rotary cutter having arranged therein ordinary flat blades, thecarbon fiber is cut discontinuously and when the carbon fiber isintroduced into a spraying step, unevenness is generated in carbon fibera real weight. Therefore, the carbon fiber is continuously cut by usinga knife at an angle specified, and whereby spraying with smallunevenness in the fiber density can be achieved. The knife angle forcontinuously cut the carbon fiber is geometrically calculated from thewidth of the carbon fiber used and the pitch of blades, and these widthand pitch are preferably in the relationship of the following formula(4). The pitch of blades in the circumferential direction is reflecteddirectly on the fiber length of the carbon fiber.Fiber length (pitch of blades) of carbon fiber=width of carbon fiberstrand×tan(90-θ)  (4)

Here, θ is the angle between the circumferential direction and thearranging direction of knife.

FIGS. 2 to 4 are examples of the knife at an angle specified, and theangle θ between the circumferential direction and the arrangingdirection of knife in these examples of the cutter is shown in thefigures.

In the case where the carbon fiber is cut to a specific length in thisstep and without cutting the carbon fiber thereafter, the composite basematerial of the present invention if formed, the average fiber length ofthe carbon fiber in the composite base material becomes the length atthe time of cutting above.

[Spraying Step]

The spraying step is a step of spraying carbon fibers obtained after thecarbon fiber strand is separated and cut to a constant length. In thespraying step, a fibrous or powdery thermoplastic resin and the carbonfiber may be sprayed at the same time. By spraying these cut carbonfiber and the like on a breathable support, a carbon fiber mat or arandom mat suitable for the composite base material of the presentinvention can be obtained.

In the case of feeding a thermoplastic resin and the carbon fiber at thesame time in the spraying step, the feed rate of the thermoplastic resinis preferably from 3 to 1,000 parts by mass per 100 parts by mass of thecarbon fiber, more preferably from 50 to 500 parts by mass per 100 partsby mass, still more preferably from 50 to 300 parts by mass per 100parts by mass.

In the spraying step, a mat having a desired thickness can be obtainedby appropriately selecting the feed rate of the carbon fiber or the feedrates of the carbon fiber and the thermoplastic resin.

Here, the carbon fibers or the carbon fibers and fibrous or powderythermoplastic resin are preferably sprayed to be orientedtwo-dimensionally. For applying opened carbon fibers while beingoriented two-dimensionally, the spraying method and the following fixingmethod are important. In the spraying method of carbon fibers, a tapertube in the form of a cone or the like is preferably used. Within thetube of a cone or the like, air diffuses and its flow rate in the tubedecreases. By utilizing this Venturi effect, carbon fibers are impartedwith a rotational force and can be spread and sprayed.

In the above-described widening step and cutting step, the degree ofopening defined in the present invention is adjusted, but the degree ofopening can also be additionally adjusted in the spraying step. Thefiber bundle is opened by blowing air to the carbon fiber introducedinto the tube. More specifically, this is a step of continuouslyintroducing cut carbon fibers into the tube, blowing a pressure airdirectly to the fibers, and thereby opening the fiber bundle separately.The degree of fiber opening can be appropriately controlled by thepressure of air or the like.

A preferable method for opening the carbon fiber is a method of blowinga compressed air directly to the carbon fiber. Specifically, air isblown from a compressed air blowing hole preferably at a wind speed of 1to 500 m/sec, and whereby the carbon fiber can be opened. Preferably, ahole of about 1 mm in diameter is formed at several portions in the tubethrough which the carbon fiber passes, and a pressure of approximatelyfrom 0.01 to 0.8 MPa is applied from the outside to directly blow thecompressed air to the fiber bundle, and whereby the fiber bundle can beopened to an arbitrary degree of fiber opening.

In order to fix the carbon fiber and the powdery or fibrousthermoplastic resin in the carbon fiber mat or random mat, air ispreferably suctioned from beneath the deposit portion of a breathablesupport on which the carbon fiber or the carbon fiber and thermoplasticresin are deposited, and thereby fixing the carbon fiber and thethermoplastic resin. Thanks to this suctioning from beneath the depositsurface, a mat having highly two-dimensional orientation can beobtained. Meanwhile, the void ratio of the carbon fiber mat or randommat after fixing is 90% or more. The fixing as used herein means a statewhere a thermoplastic resin powder or fiber is firmly bit in the mat inwhich carbon fibers are entangled and the thermoplastic resin powder orfiber does not easily fall off even when the mat is conveyed.

In this connection, when a part of the thermoplastic resin particle orthe like passes through the support due to configuration of thebreathable support and does not remain in the mat, in order to preventthis, it is also possible to separately set a nonwoven fabric or thelike on the support surface and blow the carbon fiber and thermoplasticresin particle and the like onto the nonwoven fabric and fixed.

In this case, when the nonwoven fabric is constituted by the same resinas the thermoplastic resin, the nonwoven fabric need not be separatedfrom the deposited mat and by processing the mat in the subsequentheating/pressurizing step, a fiber constituted by the nonwoven fabriccan also be utilized as a part of the thermoplastic resin to be servedas the matrix of a composite material.

By the above-described processing in the spraying step, a carbon fibermat or random mat in which carbon fibers are two-dimensionally randomlyoriented, can be obtained.

[Conveying Step]

The conveying step is a step of conveying the random mat obtained in thespraying step above or a step of conveying the carbon fiber mat obtainedin the spraying step above and in the course of conveyance, feeding asheet form thermoplastic resin in a molten state to one surface or bothsurfaces of the carbon fiber mat.

When the breathable support described in the spraying step isconstituted by a conveyor composed of a net and the carbon fiber or amixture of the carbon fiber and the thermoplastic resin is depositedthereon while continuously moving the support in one direction, andthereby a carbon fiber mat or a random mat can be continuously formed.

In the case of spraying only carbon fibers in the spraying step, amechanism of feeding the sheet form thermoplastic resin in a moltenstate to one surface or both surfaces of the carbon fiber mat isdisposed. The method for feeding the molten thermoplastic resin is amethod where a thermoplastic resin to be melted/conveyed by an extruderor the like, or a thermoplastic resin containing various additives asneeded, is fed onto the carbon fiber mat in a sheet form and in a moltenstate at a specific feed rate for a specific time to obtain one havinggiven width and thickness by using a T-die or the like. In the case offeeding the thermoplastic resin onto both surfaces of the carbon fibermat, this step is practiced by feeding the molten thermoplastic resinsheet onto a heat-resistant belt by the method above, continuouslydisposing the carbon fiber mat thereon while keeping its form, andfeeding the molten thermoplastic resin sheet similarly also onto thecarbon fiber mat.

[Heating/Pressurizing Step]

The heating/pressurizing step is a step of heating and pressurizing therandom mat conveyed as above or the carbon fiber mat adhered to thesheet form thermoplastic resin in a molten state to obtain a compositebase material having a void ratio of more than 7 vol % and less than 100vol %.

For making up the composite base material of the present invention byheating/pressurizing the above-described random mat or the like a knownmethod of heating/pressurizing a thermoplastic resin or a compositematerial thereof can be used, and the method may either a method by abatch-type apparatus or a method by a continuous apparatus.

The pressurizing method in the heating/pressurizing step is notparticularly limited but includes, preferably, a method involvingcontrol of the gap or applied pressure by a roller, a belt press or thelike. In the case of applying pressure by means of a roller, thepressure is preferably applied by previously adjusting the gap distanceof rollers so as to provide a composite base material having anobjective void ratio. As a specific example, in the case where a pair ofupper and lower rollers located with a gap is used as the pressurizingapparatus, and the random mat or the like is held in and passed throughthe gap between the paired rollers and thereby pressurized, in formula(3):Void ratio (Vr)=(t ₂ −t ₁)/t _(2×100)  (3)(wherein t₁ is a theoretical thickness when the composite base materialhas a void ratio of 0 vol %, which is calculated from the amounts ofcarbon fiber and thermoplastic resin contained in the composite basematerial, and t₂ is the average thickness of the composite basematerial), the gap distance of roller pairs can be regarded as theaverage thickness t₂ of the obtained composite base material. That is,in the case of applying the pressure by a roller, the gap distance ofroller pairs corresponding to the objective void ratio can be determinedfrom the relationship of formula (3). In the case of using apressurizing method other than this example, the gap distance of jigsholding the composite base material can also be regarded as the averagethickness t₂ of the obtained composite base material.

The heating method in the heating/pressurizing step is not particularlylimited but is preferably heating with an infrared heater or hot air orheating on a heated roll or heated plate. The heating temperature is notparticularly limited, but the temperature is preferably set so that thetemperature of the base material such as random mat is the melting pointof matrix resin or more and the melting point plus 100° C. or less, morepreferably the melting point of matrix resin or more and the meltingpoint plus 50° C. or less.

In the heating/pressurizing step, the processing can be more efficientlyperformed by previously heating the base material such as random mat toa temperature not less than the melting point of the thermoplastic resinas the matrix or to a temperature not less than the glass transitiontemperature thereof in the case where the thermoplastic resin isamorphous. An apparatus component part, such as roller and belt, used inthe heating/pressurizing step and to be in contact with the substratesuch as random mat, may be adjusted to a temperature not less than thesoftening point of the thermoplastic resin as the matrix or to atemperature less than the softening point. It is more preferable toperform a continuous heating/pressurizing step by adjusting at leasteither one of the components above to a temperature not less than themelting temperature of the thermoplastic resin. FIG. 5 shows a schematicview of the configuration example in the case of applying heat/pressureby means of a roller.

As the heating/pressurizing method for obtaining the composite basematerial of the present invention, a method where a plurality of rollerpairs are provided in a heating furnace having a heating source such asthe above-described infrared heater or hot air and the random mat, etc.is held in and passed through the gap between the paired rollers, issimple and preferred.

The heating/pressurizing treatment to the random mat, etc. may beperformed once or a plurality of times, and it may be also possible thata composite base material having a void ratio of from more than 7 vol %to less than 100 vol % of the present invention is obtained by one ormore heating/pressurizing treatments and this composite base material isfurther heated/pressurized to obtain a composite base material having alower void ratio of the present invention. Hereinafter, in the presentinvention, when performing the heating/pressurizing treatment aplurality of times, the treatment of first heating and pressurizing arandom mat or a carbon fiber mat adhered to the sheet form thermoplasticresin in a molten state is sometimes referred to as the first stage, andthe treatment of further heating/pressurizing the composite basematerial obtained by the treatment at the first stage is sometimesreferred to as the second stage.

The composite base material of the present invention is preferably acomposite base material obtained by performing the heating/pressurizingtreatment a plurality of times as described above, because when the voidratio of the composite base material is reduced to the target value by aplurality of heating/pressurizing treatments, a composite base materialexcellent particularly in the in-plane isotropy can be obtained. In thefollowing, as a preferred embodiment, for example, a plurality ofheating/pressurizing treatments for a random mat having a void ratio of90 vol % or more is illustrated.

At the first stage, the random mat having a void content of 90 vol % ormore is adjusted to a void ratio of from 75 vol % or more and less than90 vol %. This corresponds to adjusting the thickness of the random matto 4 times or more and less than 10 times relative to the thickness whenthe void ratio is 0 vol %. The pressure applied to the base materialhere is preferably adjusted in the range of from 0.01 to 2.0 MPa. If thevoid ratio is largely reduced by the decrement above or more, an excesspressure is applied to the random mat to cause a lack of in-planeisotropy or an operation failure in the heating/pressurizing step. Onthe contrary, if the decrease in percentage of the void ratio is toosmall, the temperature rise efficiency of the random mat is extremelyreduced, leading to a waste of energy or an increase in the length andsize of the apparatus. At the second and subsequent stages, the voidratio is sequentially decreased to become from 40 vol % or more and lessthan 80 vol %, 30 vol % or more and less than 75 vol %, and the like,and whereby a composite base material suitable for obtaining a compositematerial excellent in the in-plane isotropy is obtained.

In the heating/pressurizing step, the decrease in the void ratio by oneheating/pressurizing treatment is preferably less than 40 vol %, becausea composite material excellent in the in-plane isotropy is readilyobtained. The decrease in the void ratio is more preferably 32 vol % orless, still more preferably 23 vol % or less, yet still more preferably20 vol % or less.

In the foregoing pages, the heating/pressurizing step in the method forproducing the composite base material of the present invention isdescribed, but a composite base material having a void ratio of 90 vol %or more of the present invention can also be easily obtained only byheating without pressurization. For example, the random mat in which athermoplastic resin powder or fiber is adhered to or entangled with themat-form material in which carbon fibers are entangled with each other,has a high void ratio and in many cases, has a void ratio of 90 vol % ormore. Therefore, when such a random mat is only heated without beingpressurized, a composite base material having a void ratio of 90 vol %or more of the present invention is obtained.

After the heating/pressurizing step, the composite base material of thepresent invention may be directly used for the production of a compositematerial or may be cut into an appropriate dimension/shape before use.

More Preferred Embodiment of Composite Base Material of the PresentInvention

The composite base material of the present invention, which is acomposite base material is obtained by heating and pressurizing amat-form material in which a carbon fiber mat and a thermoplastic resinare combined, is preferably a composite base material obtained byapplying heat and pressure so that the decrease in the void ratio todoes not exceed 40 vol % in one heating and pressurizing treatment,because a composite material with reduced fiber orientation andexcellent in-plane isotropy can be obtained by using the composite basematerial. In the present invention, a composite base material obtainedby applying heat and pressure so that the decrease in the void ratio tobecome 32 vol % or less in one heating and pressurizing treatment ismore preferred; a composite base material obtained by applying heat andpressure so that the decrease in the void ratio to become 23 vol % orless is still more preferred; and a composite base material obtained byapplying heat and pressure so that the decrease in the void ratio tobecome 20 vol % or less is yet still more preferred.

The composite base material of the present invention, which is obtainedby heating and pressurizing a mat-form material in which a carbon fibermat and a thermoplastic resin are combined, is preferably a compositebase material having a void ratio of more than 7 vol % and less than 80vol %, the composite base material obtained by preparing a compositebase material having a void ratio of 60 vol % or more and furtherheating and pressurizing the composite base material so that thedecrease in the void ratio does not exceed 20 vol % in one heating andpressurizing treatment, because a composite material with more reducedfiber orientation and more excellent in-plane isotropy can be obtainedby using the composite base material.

The composite base material of the present invention, which is acomposite base material obtained by heating and pressurizing a mat-formmaterial in which a carbon fiber mat and a thermoplastic resin arecombined, is preferably a composite base material having a void ratio ofmore than 7 vol % and less than 80 vol %, preferably more than 7 vol %and less than 50 vol %, the composite material obtained by preparing acomposite base material having a void ratio of 40 vol % or more and lessthan 60 vol % and further heating and pressurizing the composite basematerial so that the decrease in the void ratio does not exceed 30 vol %in one heating and pressurizing treatment, because a composite materialwith more reduced fiber orientation and more excellent in-plane isotropycan be obtained by using the composite base material.

In the composite base material of the present invention, the carbonfiber contained therein is preferably a carbon fiber having a width of 5mm or less and a thickness of ½ or less of the width, because acomposite material with more reduced fiber orientation, more excellentin-plane isotropy and higher development ratio of physical properties ofthe carbon fiber can be obtained by using the composite base material.In the present invention, the width of the carbon fiber is a longer oneout of dimensions in two orthogonal directions in a cross-sectionperpendicular to the longitudinal direction of the carbon fiber, and thethickness of the carbon fiber is a shorter one out of those dimensions.In the case where the dimensions in two orthogonal directions in across-section perpendicular to the longitudinal direction of the carbonfiber are equal, the dimension in one arbitrary direction is taken asthe width of the carbon fiber, and the other is taken as the thicknessof the carbon fiber. The composite base material of the presentinvention, which is a composite base material obtained by heating andpressurizing a mat-form material in which a carbon fiber mat and athermoplastic resin are combined, is preferably a composite basematerial having a void ratio of from more than 7 vol % to less than 80vol % obtained by providing three or more heating and pressurizing stepsand in at least one stage, carrying out the pressurization whileapplying heat and pressure under extremely weak conditions causing nodecrease in the void ratio of the composite base material, because acomposite material with more reduced fiber orientation and moreexcellent in-plane isotropy can be obtained by using the composite basematerial. The pressurization under extremely weak conditions causing nodecrease in the void ratio of the composite base material includes, forexample, a method where at the time of heating and pressurizing thecomposite base material, the treatment is performed by setting the gapdistance of a certain roller pair to be equal to the gap distance of aroller pair at the previous stage.

[Composite Material]

The thus-obtained composite base material of the present invention isfurther pressurized, and whereby a composite material used as aprecursor to obtain a shaped product for various applications canobtained.

The composite material obtained from the composite base material of thepresent invention has a void ratio as defined in formula (3) ofpreferably from 0 vol % or more and 7 vol % or less, more preferably 0vol % or more and 3 vol % or less, and is excellent in the in-planeisotropy. The in-plane isotropy of a composite material can bequantitatively evaluated by measuring a specimen of the compositematerial for the tensile modulus in two directions orthogonal to eachother and determining the ratio therebetween. When the ratio (Eσ,hereinafter sometimes referred to as a tensile modulus ratio) obtainedby dividing a larger value out of tensile modulus values in twodirections of the composite material by a smaller value does not exceed2, the sample is evaluated as in-plane isotropic, and when the ratiodoes not exceed 1.3, the sample is evaluated as excellent in thein-plane isotropy.

As the method for obtaining a composite material from the composite basematerial of the present invention, the composite base material after theheating/pressurizing step in the above-described production method of acomposite base material may be subsequently pressurized while keeping itat a temperature not less than the softening point of the matrix resin,to obtain a composite material. At this time, the method for keeping thecomposite base material at a temperature not less than the softeningpoint of the matrix resin may be a method of promptly using thecomposite base material for the production of a composite materialbefore the temperature decreases to a temperature less than thesoftening point of the matrix resin or may be of course a method ofkeeping warm or heating the composite base material at a temperature notless than the softening point.

The composite material obtained by pressurizing or heating/pressurizingthe composite base material is preferably completed as a compositematerial by a method of finally solidifying the thermoplastic resin byproviding a cooling step of keeping the composite material at atemperature less than the softening point of the matrix resin of thecomposite base material, or the composite material after thepressurizing or heating/pressurizing step may be subsequentlypressurized while cooling it to a temperature less than the softeningpoint of the matrix resin to form a composite material.

The composite material obtained from the composite base material of thepresent invention is not particularly limited in its shape, butrepresentative examples thereof include, similarly to the composite basematerial, a plate-shaped material, among others, a substantiallyrectangular plate-shaped material, and the plate-shaped material may bea so-called long material.

[Shaped Product]

The composite material above is used as a precursor of a shaped product.The method for molding the composite material is not particularlylimited, but the composite material is molded, for example, by vacuummolding, hydraulic molding, hot pressing or cold pressing, and whereby ashaped product having a shape necessary for the usage can be suitablyobtained.

At the time of molding of the composite material, a shaped productdiffering in the thickness according to the purpose can be obtained byappropriately adding a plurality of layers or a thermoplastic resinentirely or partially to the composite material. The thermoplastic resinis not particularly limited and may be the same resin as the matrix inthe composite base material or may be different therefrom. Furthermore,the form of the resin used may also be a molten resin or a fibrous,powdery or filmy resin. Specific examples of the thermoplastic resinadded at the time of molding are the same as those described in theparagraph of the thermoplastic resin in the composite base material.

[Layered Body]

As the composite material of the present invention, a layered bodyobtained by further layering the composite material of the presentinvention or a unidirectional carbon fiber material on a part or theentirety of at least one surface of the composite material of thepresent invention is also preferred. The unidirectional material isconstituted by a thermoplastic resin and a unidirectional material inwhich continuous carbon fibers are aligned in one direction. Theunidirectional material may be a stacked body obtained by stacking aplurality of unidirectional materials or may be a multiaxial wovenfabric in which a stacked body (multiaxial woven fabric base material)obtained by stacking, at different angles, sheets formed fromfiber-reinforced material bundles aligned in one direction is stitchedwith a stitching yarn, such as nylon yarn, polyester yarn and glassfiber yarn, penetrating in the thickness direction and reciprocatingalong the surface direction between the front side and the back side ofthe stacked body.

The average fiber diameter of the carbon fiber constituting theunidirectional material layer is preferably from 3 to 12 μm, morepreferably from 5 to 7 μm.

The content of the thermoplastic resin in the unidirectional material ispreferably from 3 to 400 parts by mass per 100 parts by mass of thecarbon fiber. The content of the thermoplastic resin is more preferablyfrom 10 to 100 parts by mass per 100 parts by mass of the carbon fiber.

The thermoplastic resin constituting the unidirectional material may bethe same as or different from the matrix in the composite material.Specific examples of the thermoplastic resin are the same as thosedescribed in the paragraph of the thermoplastic resin in the compositebase material.

The layering method is not particularly limited but includes, forexample, a method by heat welding or pressure bonding.

In the case of heat welding, it is also preferred that a base materialand a unidirectional material are combined and heated in the step ofheating the random mat. The adhesion portion between the unidirectionalmaterial and the base material may a part of the surface or the entiresurface. By combining the composite material of the present inventionand a unidirectional material, the mechanical characteristics of aportion required in the shaped product can be intensively enhancedwithout involving an excessive increase in the weight.

EXAMPLES

Examples are illustrated below, but the present invention is not limitedthereto, and many modifications can be made within the technical idea ofthe present invention by one having ordinary knowledge in this field.The densities of the carbon fibers or thermoplastic resins used in thefollowing Examples and Comparative Examples are as follows.

PAN-Based carbon fiber “Tenax” (registered trademark) STS40-24KS: 1.75g/cm³

Polybutylene terephthalate resin: 1.31 g/cm³

Polycarbonate: 1.20 g/cm³

Polyamide 6: 1.14 g/cm³

[Method for Determining Void Ratio]

1) The theoretical thickness (t₁) per unit area (1 m²) of the compositebase material having a void ratio of 0% obtained from the random mat iscalculated from the contents of carbon fiber and thermoplastic resincontained in the random mat.

2) The thickness in the entirety or given area of the random max ismeasured down to 1/100 mm at 100 points/m² by using a caliper withoutapplying a load, and the average thickness of the random mat wasdetermined from the obtained values. This average thickness is regardedas t₂, and the void ratio of the random mat is calculated according toformula (3) by using the determined average thickness together with thetheoretical thickness (t₁) at a void ratio of 0% of the composite basematerial determined in the paragraph above. The obtained value isdefined as the initial void ratio.

3) The average thickness of the composite vase material at the time oftreatment of sequentially decreasing the void ratio in theheating/pressurizing step of the composite base material is designatedas t₂, and the void ratio (Vr) of the composite base material isdetermined from the void content (t₂−t₁) according to the followingformula (3):Vr=(t ₂ −t ₁)/t ₂×100  (3)(wherein t₁ is the theoretical thickness calculated from the amount ofcarbon fiber and thermoplastic resin contained in the composite basematerial when the void ratio of the composite base material is 0 vol %,and t₂ is the average thickness of the composite base material.

Meanwhile, as for t₂ at each stage in the heating and pressurizing step,the gap distance of a roller pair applying pressure is taken as theaverage thickness (t₂) of the composite base material.

In Examples, the decrement value of the void ratio in a certainheating/pressurizing treatment is sometimes not consistent with thesubtraction result of the void ratio between before and after theheating/pressurizing treatment. This is because the void ratio of thecomposite base material is expressed by a value rounded off to thenearest whole number. However, the employed decrement value of the voidratio in the heating/pressurizing treatment at each stage is a numericalvalue rounded off to the nearest whole number of the calculation resultobtained by using the void ratio value not rounded off to the nearestwhole number. As a result, an error is sometimes produced.

[Method for Determining Ratio of Carbon Fiber Bundle (A) to Total Amountof Fibers in Composite Base Material]

1) The composite base material is cut out into 100 mm×100 mm and treatedin a furnace at 500° C.×for about 1 hour to remove the resin.

2) All fiber bundles are extracted with tweezers from the composite basematerial after removal of the resin.

3) The length (L_(i)) and weight (W_(i)) of individual fiber bundles aremeasured on all fiber bundles and recorded. Fiber bundles small to suchan extent as cannot be extracted with tweezers are collectively measuredfor the weight (W_(k)) at the end. At this time, a balance capable ofmeasuring down to 1/100 mg is used. The critical number of single fibersis calculated from the fiber diameter (D) of the carbon fiber used inthe random mat, and the carbon fiber bundle (A) having carbon fibers ofnot less than the critical number of single fibers is separated fromothers. Incidentally, in the case where two or more kinds of carbonfibers are used, the fibers are divided by the kind, and the measurementand evaluation are performed on each kind of fiber.

4) After measuring on all sorts, the average number (N) of fibers in thecarbon fiber bundle (A) is determined according to the followingcalculation. The number (N_(i)) of fibers in each carbon fiber bundlecan be determined from the fineness (F) of the carbon fiber usedaccording to formula (5):N _(i) =Wi/L _(i) ×F)  (5)

The average number (N) of fibers in the carbon fiber bundle (A) isdetermined from the number (I) of bundles of the carbon fiber bundle (A)according to the following formula (6):N=ΣNi/I  (6)

In addition, the ratio (V_(R)) of the carbon fiber bundle (A) to allfibers of the mat is determined using the fiber specific gravity (ρ) ofthe carbon fiber according to the following formula (7):V _(R)=Σ(W _(i)/ρ)×100/((W _(k) +ΣW _(i))/ρ)  (7)

The width and thickness of the carbon fiber contained in the compositebase material can also be measured as described above by removing theresin from the composite base material and extracting carbon fibers.

[Analysis of Fiber Orientation in Composite Material]

As the method for measuring the in-plane isotropy of the carbon fiberafter molding the composite material, a tensile modulus is measured byperforming a tensile test based on an arbitrary direction of a shapedplate and a direction orthogonal thereto, and a ratio (sometimesreferred to as Eδ or a tensile modulus ratio) obtained by dividing thelarger value by the smaller value out of the measured values of tensilemodulus is measured, and whereby the in-plane isotropy can be confirmed.A tensile modulus ratio closer to 1 indicates that the material is moreexcellent in the in-plane isotropy.

Example 1

As the carbon fiber, PAN-based carbon fiber “Tenax” (registeredtrademark) STS40-24KS (average fiber diameter: 7 μm, strand width: 10mm) produced by TOHO TENAX Co., Ltd was used. This carbon fiber strandwas widened to a width of 15 to 20 mm, furthermore slit to a width of0.8 mm by using a longitudinal slitter and then cut to a fiber length of20 mm. As the cutting device, a rotary cutter having a cementedcarbide-made spiral knife provided on the surface thereof was used.

A strand passed through the rotary cutter was introduced into a flexibletransport pipe arranged just under the rotary cutter and subsequentlyintroduced into a spraying device (air blowing nozzle). As the sprayingdevice, a double tube was produced by welding SUS 304-made nipplesdifferent in the diameter and used. Small holes were provided in theinner tube of the double tube, and compressed air was fed between theinner tube and the outer tube by using a compressor. At this time, thewind velocity of air from the small hole was 50 m/sec. A tapered tubewith the diameter increasing downward was welded to a lower part of thedouble tube.

A matrix resin was fed from the side surface of the tapered tube. As thematrix resin, a particle of nylon 6 resin “A1030” produced by UnitikaLtd. was used.

A breathable support (hereinafter, referred to as a fixing net) movablein a given direction was disposed under the tapered tube outlet andsuctioned from below by a blower, and a mixture of the cut carbon fiberand the nylon resin was deposited in a band form on the fixing net whilereciprocating the flexible transport pipe and the tapered tube in thewidth direction of the fixing net moving at a constant speed.

Thereafter, the feed rate of carbon fiber and the feed rate of matrixresin were set to 212 g/min and 320 g/min, respectively, and theapparatus was operated, as a result, a random mat resulting from mixingof the carbon fiber and the matrix fiber (thermoplastic resin) on thefixing net with no unevenness was continuously formed on the fixing netmoving in a given direction. The carbon fiber a real weight of therandom mat was 265 g/m².

The obtained random mat was examined for the ratio of the carbon fiberbundle (A) and the average number (N) of fibers. Then, the criticalnumber of single fibers defined by formula (1) was 86, the ratio of thecarbon fiber bundle (A) to the total amount of fibers in the mat was 80vol %, and the average number (N) of fibers in the carbon fiber bundle(A) was 600. In addition, the nylon 6 particles were uniformly dispersedand firmly fixed in the carbon fiber with almost no unevenness. Theinitial void ratio was 91 vol %.

The random mat obtained above was subjected to a heating/pressurizingtreatment by using an apparatus constituted by a steel belt, a rollerand a heating furnace. This apparatus has a structure where a pluralityof upper and lower roller pairs each spaced by a gap are disposed in theheating furnace and the steel belt is continuously passed therethroughin the manner of holding the random mat in the roller gap. The pressureacting on the random mat through the steel belt is adjusted by adjustingthe gap between rollers disposed in the heating furnace to allow thecomposite base material to have the objective void ratio.

As described below, the steel belt clamping 6 random mats was passedthrough a plurality of roller gaps set to give a surface temperature of260 to 360° C., so that the final composite material can have athickness of 3 mm. The heating/pressurizing treatment for obtaining acomposite base material was performed in 7 stages by using 7 rollerpairs disposed in the steel belt running direction in the heatingfurnace and by gradually decreasing the void ratio in a stepwise mannerof 85 vol %, 80 vol %, 75 vol %, 70 vol %, 58 vol %, 47 vol % and 29 vol% relative to the initial void ratio of 91 vol % of the random mat, acomposite base material in which a thermoplastic resin was firmly fixedto a carbon fiber was obtained without causing a process failure. In oneheating/pressurizing treatment, the void ratio was most decreased at theseventh stage and decreased there by 18 vol %. When the composite basematerial having a void ratio of 60 vol % or more was furtherheated/pressurized, the void ratio was most decreased at the fifth stagein one heating/pressurizing treatment and decreased there by 12 vol %.When the composite base material having a void ratio of 40 vol % or moreand less than 60 vol % was further heated/pressurized, the void ratiowas most decreased at the seventh stage in one heating/pressurizingtreatment and decreased there by 18 vol %.

The high-temperature composite base material obtained above wassubjected to a cooling/pressurizing step using a pair of cooling rollersat a temperature not more than the softening point of the thermoplasticresin. Then, a composite material plate having a thickness of 3 mm wasobtained. A test piece was cut out from the obtained composite materialplate and measured in accordance with JIS7164, as a result, the tensilemodulus ratio between an arbitrary direction and a direction orthogonalthereto was 1.07.

Meanwhile, the average fiber length of carbon fibers in the obtainedcomposite base material or composite material was 20 mm that is thelength when the carbon fiber strand was cut. Similarly, the width of thecarbon fiber in the obtained composite base material or compositematerial was significantly narrower than 5 mm, and the thickness of thecarbon fiber was ½ or less of the width.

Example 2

Using the random mat described in Example 1, as described below, a steelbelt clamping 6 random mats was passed through gaps of a plurality ofroller pairs set to give a surface temperature of 260 to 360° C., sothat the final composite material can have a thickness of 3 mm. Theheating/pressurizing treatment for obtaining a composite base materialwas performed in 6 stages by using 6 roller pairs disposed in the steelbelt running direction in the heating furnace and by graduallydecreasing the void ratio in a stepwise manner of 83 vol %, 78 vol %, 67vol %, 50 vol %, 33 vol % and 19 vol % relative to the initial voidratio of 91 vol % of the random mat, a composite base material in whicha thermoplastic resin was firmly fixed to a carbon fiber was obtainedwithout causing a process failure. In one heating/pressurizingtreatment, the void ratio was most decreased at the fourth and fifthstages, and in both of these stages, the void ratio was decreased by 17vol %. When the composite base material having a void ratio of 60 vol %or more was further heated/pressurized, the void ratio was mostdecreased at the fourth stage in one heating/pressurizing treatment,where the void ratio was decreased by 17 vol %. When the composite basematerial having a void ratio of 40 vol % or more and less than 60 vol %was further heated/pressurized, the void ratio was most decreased at thefifth stage in one heating/pressurizing treatment, where the void ratiowas decreased by 17 vol %.

The high-temperature composite base material obtained above wassubjected to a cooling/pressurizing step using a pair of cooling rollersat a temperature not more than the softening point of the thermoplasticresin. Then, a composite material plate having a thickness of 3 mm wasobtained. A test piece was cut out from the obtained composite materialplate and measured in accordance with JIS7164, as a result, the tensilemodulus ratio between an arbitrary direction and a direction orthogonalthereto was 1.12.

Meanwhile, the average fiber length of carbon fibers in the obtainedcomposite base material or composite material was 20 mm that is thelength when the carbon fiber strand was cut. Similarly, the width of thecarbon fiber in the obtained composite base material or compositematerial was significantly narrower than 5 mm, and the thickness of thecarbon fiber was ½ or less of the width.

Example 3

Using the random mat described in Example 1, as described below, a steelbelt clamping 6 random mats was passed through gaps of a plurality ofroller pairs set to give a surface temperature of 260 to 360° C., sothat the final composite material can have a thickness of 3 mm. Theheating/pressurizing treatment for obtaining a composite base materialwas performed in 5 stages by using 5 roller pairs disposed in the steelbelt running direction in the heating furnace and by graduallydecreasing the void ratio in a stepwise manner of 80 vol %, 78 vol %, 60vol %, 41 vol % and 23 vol % relative to the initial void ratio of 91vol % of the random mat, a composite base material in which athermoplastic resin was firmly fixed to a carbon fiber was obtainedwithout causing a process failure. In one heating/pressurizingtreatment, the void ratio was most decreased at the fourth stage, and inthis stage, the void ratio was decreased by 19 vol %. When the compositebase material having a void ratio of 60 vol % or more was furtherheated/pressurized, the void ratio was most decreased at the fourthstage in one heating/pressurizing treatment, where the void ratio wasdecreased by 19 vol %. When the composite base material having a voidratio of 40 vol % or more and less than 60 vol % was furtherheated/pressurized, the void ratio was most decreased at the fifth stagein one heating/pressurizing treatment, where the void ratio wasdecreased by 18 vol %.

The high-temperature composite base material obtained above wassubjected to a cooling/pressurizing step using a pair of cooling rollersat a temperature not more than the softening point of the thermoplasticresin. Then, a composite material plate having a thickness of 3 mm wasobtained. A test piece was cut out from the obtained composite materialplate and measured in accordance with JIS7164, as a result, the tensilemodulus ratio between an arbitrary direction and a direction orthogonalthereto was 1.09.

Meanwhile, the average fiber length of carbon fibers in the obtainedcomposite base material or composite material was 20 mm that is thelength when the carbon fiber strand was cut. Similarly, the width of thecarbon fiber in the obtained composite base material or compositematerial was significantly narrower than 5 mm, and the thickness of thecarbon fiber was ½ or less of the width.

Comparative Example 1

Using the random mat described in Example 1, as described below, a steelbelt clamping 6 random mats was passed through gaps of a plurality ofroller pairs set to give a surface temperature of 260 to 360° C., sothat the final composite material can have a thickness of 3 mm. Theheating/pressurizing treatment for obtaining a composite base materialwas performed in 6 stages by using 6 roller pairs disposed in the steelbelt running direction in the heating furnace and by graduallydecreasing the void ratio in a stepwise manner of 80 vol %, 78 vol %, 60vol %, 50 vol %, 33 vol % and 7 vol % relative to the initial void ratioof 91 vol % of the random mat, a composite base material was obtainedwithout causing a process failure. In one heating/pressurizingtreatment, the void ratio was most decreased at the sixth stage anddecreased there by 26 vol %. When the composite base material having avoid ratio of 60 vol % or more was further heated/pressurized, the voidratio was most decreased at the third stage in one heating/pressurizingtreatment, where the void ratio was decreased by 18 vol %. When thecomposite base material having a void ratio of 40 vol % or more and lessthan 60 vol % was further heated/pressurized, the void ratio was mostdecreased at the fifth stage in one heating/pressurizing treatment,where the void ratio was decreased by 17 vol %.

The high-temperature composite base material obtained above wassubjected to a cooling/pressurizing step using a pair of cooling rollersat a temperature not more than the softening point of the thermoplasticresin. Then, a composite material plate having a thickness of 3 mm wasobtained. The obtained composite material plate was measured inaccordance with JS7164, as a result, the tensile modulus ratio betweenan arbitrary direction and a direction orthogonal thereto was 1.43. Byobserving the surface of the composite material with an eye, it wasconfirmed that carbon fibers are aligned along the steel belt runningdirection in the production process of the composite base material.

Reference Example 1

Using the random mat described in Example 1, as described below, a steelbelt clamping 6 random mats was passed through gaps of a plurality ofroller pairs set to give a surface temperature of 260 to 360° C., sothat the final composite material can have a thickness of 3 mm. Aheating/pressurizing treatment for obtaining a composite base materialwas performed using 1 roller pair disposed in the steel belt runningdirection in the heating furnace with an attempt to obtain a compositebase material having a void ratio of 67 vol % from the random mat havingan initial void ratio of 91 vol %, but a process failure occurred, thatis, the random mat clamped by the steel belt did not proceed downstreamof the roller gap, and a composite base material was not able to beobtained.

Reference Example 2

Using the random mat described in Example 1, a steel belt clamping 6random mats was passed through gaps of a plurality of roller pairs setto give a surface temperature of 260 to 360° C., so that the finalcomposite material can have a thickness of 3 mm. A heating/pressurizingtreatment for obtaining a composite base material was performed using 2roller pairs disposed in the steel belt running direction in the heatingfurnace with an attempt to decrease the void ratio in a stepwise mannerof 83 vol % and 50 vol % relative to the random mat having an initialvoid ratio of 91 vol %, but the same process failure as in ReferenceExample 1 occurred in the heating/pressurization at the second stage,and a composite base material usable for obtaining a composite materialwas not able to be obtained.

Example 4

A random mat having a carbon fiber a real weight of 294 g/m² and aninitial void ratio of 88 vol % was obtained by performing the operationin the same manner as in the production of a random mat in Example 1except for changing the feed rate of carbon fiber to 236 g/min andchanging the feed rate of nylon 6 resin “A1030” as the matrix resin to275 g/min. The ratio of the carbon fiber bundle (A) and the averagenumber (N) of fibers in the random mat obtained were the same as thosein Example 1. In the obtained random mat, the nylon 6 particles wereuniformly dispersed and fixed in the carbon fiber with almost nounevenness.

Using the random mat obtained above, as described below, a steel beltclamping 8 random mats was passed through gaps of a plurality of rollerpairs set to give a surface temperature of 260 to 360° C., so that thefinal composite material can have a thickness of 3.7 mm. Theheating/pressurizing treatment for obtaining a composite base materialwas performed in 5 stages by using 3 pairs out of 5 roller pairsdisposed in the steel belt running direction in the heating furnace,where in two stages out of those stages, the treatment was performedunder an extremely weak pressurizing condition involving no decrease inthe void ratio, and by gradually decreasing the void ratio in a stepwisemanner of 59 vol %, 59 vol %, 38 vol %, 38 vol % and 8 vol % relative tothe initial void ratio of 88 vol % of the random mat, a composite basematerial in which a thermoplastic resin was firmly fixed to a carbonfiber was obtained without causing a process failure. In oneheating/pressurizing treatment, the void ratio was most decreased at thefifth stage where the void ratio was decreased by 31 vol %. When thecomposite base material having a void ratio of 60 vol % or more wasfurther heated/pressurized, the void ratio was not decreased. When thecomposite base material having a void ratio of 40 vol % or more and lessthan 60 vol % was further heated/pressurized, the void ratio was mostdecreased at the third stage in one heating/pressurizing treatment,where the void ratio was decreased by 21 vol %.

The high-temperature composite base material obtained above wassubjected to a cooling/pressurizing step using a pair of cooling rollersat a temperature not more than the softening point of the thermoplasticresin. Then, a composite material plate having a thickness of 3.7 mm wasobtained. A test piece was cut out from the obtained composite materialplate and measured in accordance with JIS7164, as a result, the tensilemodulus ratio between an arbitrary direction and a direction orthogonalthereto was 1.18.

Meanwhile, the average fiber length of carbon fibers in the obtainedcomposite base material or composite material was 20 mm that is thelength when the carbon fiber strand was cut. Similarly, the width of thecarbon fiber in the obtained composite base material or compositematerial was significantly narrower than 5 mm, and the thickness of thecarbon fiber was ½ or less of the width.

Example 5

Using the random mat described in Example 4, as described below, a steelbelt clamping 6 random mats was passed through gaps of a plurality ofroller pairs set to give a surface temperature of 260 to 360° C., sothat the final composite material can have a thickness of 2.8 mm. Theheating/pressurizing treatment for obtaining a composite base materialwas performed in 6 stages by using 6 roller pairs disposed in the steelbelt running direction in the heating furnace, where in two stages outof those stages, the treatment was performed under an extremely weakpressurizing condition involving no decrease in the void ratio, and bygradually decreasing the void ratio in a stepwise manner of 69 vol %, 69vol %, 53 vol %, 53 vol %, 30 vol % and 20 vol % relative to the initialvoid ratio of 88 vol % of the random mat, a composite base material inwhich a thermoplastic resin was firmly fixed to a carbon fiber wasobtained without causing a process failure. In one heating/pressurizingtreatment, the void ratio was most decreased at the fifth stage anddecreased there by 23 vol %. When the composite base material having avoid ratio of 60 vol % or more was further heated/pressurized, the voidratio was most decreased at the third stage in one heating/pressurizingtreatment, where the void ratio was decreased by 16 vol %. When thecomposite base material having a void ratio of 40 vol % or more and lessthan 60 vol % was further heated/pressurized, the void ratio was mostdecreased at the fifth stage in one heating/pressurizing treatment,where the void ratio was decreased by 23 vol %.

The high-temperature composite base material obtained above wassubjected to a cooling/pressurizing step using a pair of cooling rollersat a temperature not more than the softening point of the thermoplasticresin. Then, a composite material plate having a thickness of 2.8 mm wasobtained. A test piece was cut out from the obtained composite materialplate and measured in accordance with JIS7164, as a result, the tensilemodulus ratio between an arbitrary direction and a direction orthogonalthereto was 1.09.

Meanwhile, the average fiber length of carbon fibers in the obtainedcomposite base material or composite material was 20 mm that is thelength when the carbon fiber strand was cut. Similarly, the width of thecarbon fiber in the obtained composite base material or compositematerial was significantly narrower than 5 mm, and the thickness of thecarbon fiber was ½ or less of the width.

Example 6

Using the random mat described in Example 4, as described below, a steelbelt clamping 5 random mats was passed through gaps of a plurality ofroller pairs set to give a surface temperature of 260 to 360° C., sothat the final composite material can have a thickness of 2.3 mm. Theheating/pressurizing treatment for obtaining a composite base materialwas performed in 6 stages by using 6 roller pairs disposed in the steelbelt running direction in the heating furnace, where in two stages outof those stages, the treatment was performed under an extremely weakpressurizing condition involving no decrease in the void ratio, and bygradually decreasing the void ratio in a stepwise manner of 74 vol %, 74vol %, 62 vol %, 62 vol %, 43 vol % and 16 vol % relative to the initialvoid ratio of 88 vol % of the random mat, a composite base material inwhich a thermoplastic resin was firmly fixed to a carbon fiber wasobtained without causing a process failure. In one heating/pressurizingtreatment, the void ratio was most decreased at the sixth stage anddecreased there by 26 vol %. When the composite base material having avoid ratio of 60 vol % or more was further heated/pressurized, the voidratio was most decreased at the third stage in one heating/pressurizingtreatment, where the void ratio was decreased by 16 vol %. When thecomposite base material having a void ratio of 40 vol % or more and lessthan 60 vol % was further heated/pressurized, the void ratio was mostdecreased at the sixth stage in one heating/pressurizing treatment,where the void ratio was decreased by 26 vol %.

The high-temperature composite base material obtained above wassubjected to a cooling/pressurizing step using a pair of cooling rollersat a temperature not more than the softening point of the thermoplasticresin. Then, a composite material plate having a thickness of 2.3 mm wasobtained. A test piece was cut out from the obtained composite materialplate and measured in accordance with JIS7164, as a result, the tensilemodulus ratio between an arbitrary direction and a direction orthogonalthereto was 1.13.

Meanwhile, the average fiber length of carbon fibers in the obtainedcomposite base material or composite material was 20 mm that is thelength when the carbon fiber strand was cut. Similarly, the width of thecarbon fiber in the obtained composite base material or compositematerial was significantly narrower than 5 mm, and the thickness of thecarbon fiber was ½ or less of the width.

Example 7

Using the random mat described in Example 4, as described below, a steelbelt clamping 4 random mats was passed through gaps of roller pairs setto give a surface temperature of 260 to 360° C., so that the finalcomposite material can have a thickness of 1.9 mm. Theheating/pressurizing treatment for obtaining a composite base materialwas performed in 6 stages by using 6 roller pairs disposed in the steelbelt running direction in the heating furnace, where in two stages outof those stages, the treatment was performed under an extremely weakpressurizing condition involving no decrease in the void ratio, and bygradually decreasing the void ratio in a stepwise manner of 79 vol %, 79vol %, 68 vol %, 68 vol %, 53 vol % and 21 vol % relative to the initialvoid ratio of 88 vol % of the random mat, a composite base material inwhich a thermoplastic resin was firmly fixed to a carbon fiber wasobtained without causing a process failure. In one heating/pressurizingtreatment, the void ratio was most decreased at the sixth stage anddecreased there by 32 vol %. When the composite base material having avoid ratio of 60 vol % or more was further heated/pressurized, the voidratio was most decreased at the fifth stage in one heating/pressurizingtreatment, where the void ratio was decreased by 16 vol %. When thecomposite base material having a void ratio of 40 vol % or more and lessthan 60 vol % was further heated/pressurized, the void ratio was mostdecreased at the sixth stage in one heating/pressurizing treatment,where the void ratio was decreased by 32 vol %.

The high-temperature composite base material obtained above wassubjected to a cooling/pressurizing step using a pair of cooling rollersat a temperature not more than the softening point of the thermoplasticresin. Then, a composite material plate having a thickness of 1.9 mm wasobtained. A test piece was cut out from the obtained composite materialplate and measured in accordance with JIS7164, as a result, the tensilemodulus ratio between an arbitrary direction and a direction orthogonalthereto was 1.07.

Meanwhile, the average fiber length of carbon fibers in the obtainedcomposite base material or composite material was 20 mm that is thelength when the carbon fiber strand was cut. Similarly, the width of thecarbon fiber in the obtained composite base material or compositematerial was significantly narrower than 5 mm, and the thickness of thecarbon fiber was ½ or less of the width.

Example 8

A random mat having a carbon fiber a real weight of 945 g/m² and aninitial void ratio of 93 vol % was obtained by performing the operationin the same manner as in the production of a random mat in Example 1except for changing the feed rate of carbon fiber to 945 g/min andchanging the feed rate of nylon 6 resin “A1030” as the matrix resin to1,102 g/min. The ratio of the carbon fiber bundle (A) and the averagenumber (N) of fibers in the random mat obtained were the same as thosein Example 1. In the obtained random mat, the nylon 6 particles wereuniformly dispersed and fixed in the carbon fiber with almost nounevenness.

Using the random mat obtained above, as described below, a steel beltclamping 1 random mat was passed through gaps of roller pairs set togive a surface temperature of 260 to 360° C., so that the finalcomposite material can have a thickness of 1.5 mm. Theheating/pressurizing treatment for obtaining a composite base materialwas performed in 6 stages by using 6 roller pairs disposed in the steelbelt running direction in the heating furnace, where in two stages outof those stages, the treatment was performed under an extremely weakpressurizing condition involving no decrease in the void ratio, and bygradually decreasing the void ratio in a stepwise manner of 75 vol %, 75vol %, 63 vol %, 63 vol %, 50 vol % and 25 vol % relative to the initialvoid ratio of 93 vol % of the random mat, a composite base material inwhich a thermoplastic resin was firmly fixed to a carbon fiber wasobtained without causing a process failure. In one heating/pressurizingtreatment, the void ratio was most decreased at the sixth stage anddecreased there by 25 vol %. When the composite base material having avoid ratio of 60 vol % or more was further heated/pressurized, the voidratio was most decreased at the fifth stage in one heating/pressurizingtreatment, where the void ratio was decreased by 13 vol %. When thecomposite base material having a void ratio of 40 vol % or more and lessthan 60 vol % was further heated/pressurized, the void ratio was mostdecreased at the fifth stage in one heating/pressurizing treatment,where the void ratio was decreased by 25 vol %.

The high-temperature composite base material obtained above wassubjected to a cooling/pressurizing step using a pair of cooling rollersat a temperature not more than the softening point of the thermoplasticresin. Then, a composite material plate having a thickness of 1.5 mm wasobtained. A test piece was cut out from the obtained composite materialplate and measured in accordance with JIS7164, as a result, the tensilemodulus ratio between an arbitrary direction and a direction orthogonalthereto was 1.04.

Meanwhile, the average fiber length of carbon fibers in the obtainedcomposite base material or composite material was 20 mm that is thelength when the carbon fiber strand was cut. Similarly, the width of thecarbon fiber in the obtained composite base material or compositematerial was significantly narrower than 5 mm, and the thickness of thecarbon fiber was ½ or less of the width.

Example 9

A random mat having a carbon fiber a real weight of 1,260 g/m² and aninitial void ratio of 91 vol % was obtained by performing the operationin the same manner as in the production of a random mat in Example 1except for changing the feed rate of carbon fiber to 1,260 g/min andusing, as the matrix resin, a polycarbonate (Panlite (registeredtrademark) L-1225Y, produced by Teijin Chemicals Ltd.) at a feed rate of1,560 g/min in place of nylon 6 resin “A1030”. The ratio of the carbonfiber bundle (A) and the average number (N) of fibers in the random matobtained were the same as those in Example 1. In the obtained randommat, the polycarbonate particles were uniformly dispersed and fixed inthe carbon fiber with almost no unevenness.

Using the random mat obtained above, as described below, a steel beltclamping 1 random mat was passed through gaps of roller pairs set togive a surface temperature of 260 to 360° C., so that the finalcomposite material can have a thickness of 2.0 mm. Theheating/pressurizing treatment for obtaining a composite base materialwas performed in 6 stages by using 6 roller pairs disposed in the steelbelt running direction in the heating furnace, and by graduallydecreasing the void ratio in a stepwise manner of 80 vol %, 67 vol %, 50vol %, 33 vol %, 20 vol % and 9 vol % relative to the initial void ratioof 91 vol % of the random mat, a composite base material in which athermoplastic resin was firmly fixed to a carbon fiber was obtainedwithout causing a process failure. In one heating/pressurizingtreatment, the void ratio was most decreased at the third and fourthstages, and in both of these stages, the void ratio was decreased by 17vol %. When the composite base material having a void ratio of 60 vol %or more was further heated/pressurized, the void ratio was mostdecreased at the third stage in one heating/pressurizing treatment,where the void ratio was decreased by 17 vol %. When the composite basematerial having a void ratio of 40 vol % or more and less than 60 vol %was further heated/pressurized, the void ratio was most decreased at thefourth stage in one heating/pressurizing treatment, where the void ratiowas decreased by 17 vol %.

The high-temperature composite base material obtained above wassubjected to a cooling/pressurizing step using a pair of cooling rollersat a temperature not more than the softening point of the thermoplasticresin. Then, a composite material plate having a thickness of 2.0 mm wasobtained. A test piece was cut out from the obtained composite materialplate and measured in accordance with JIS7164, as a result, the tensilemodulus ratio between an arbitrary direction and a direction orthogonalthereto was 1.08.

Meanwhile, the average fiber length of carbon fibers in the obtainedcomposite base material or composite material was 20 mm that is thelength when the carbon fiber strand was cut. Similarly, the width of thecarbon fiber in the obtained composite base material or compositematerial was significantly narrower than 5 mm, and the thickness of thecarbon fiber was ½ or less of the width.

Example 10

A random mat having a carbon fiber a real weight of 1,260 g/m² and aninitial void ratio of 91 vol % was obtained by performing the operationin the same manner as in the production of a random mat in Example 1except for changing the feed rate of carbon fiber to 1,260 g/min andusing, as the matrix resin, a polybutylene terephthalate resin (Duranex(registered trademark) 2002, produced by WinTech Polymer Ltd.,hereinafter sometimes simply referred to as PBT) at a feed rate of 1,703g/min in place of nylon 6 resin “A1030”. The ratio of the carbon fiberbundle (A) and the average number (N) of fibers in the random matobtained were the same as those in Example 1. In the obtained randommat, the PBT particles were uniformly dispersed and fixed in the carbonfiber with almost no unevenness.

Using the random mat obtained above, as described below, a steel beltclamping 1 random mat was passed through gaps of roller pairs set togive a surface temperature of 260 to 400° C., so that the finalcomposite material can have a thickness of 2.0 mm. Theheating/pressurizing treatment for obtaining a composite base materialwas performed in 5 stages by using 5 roller pairs disposed in the steelbelt running direction in the heating furnace, and by graduallydecreasing the void ratio in a stepwise manner of 72 vol %, 60 vol %, 43vol %, 20 vol % and 10 vol % relative to the initial void ratio of 91vol % of the random mat, a composite base material in which athermoplastic resin was firmly fixed to a carbon fiber was obtainedwithout causing a process failure. In one heating/pressurizingtreatment, the void ratio was most decreased at the fourth stage wherethe void ratio was decreased by 23 vol %. When the composite basematerial having a void ratio of 60 vol % or more was furtherheated/pressurized, the void ratio was most decreased at the third stagein one heating/pressurizing treatment, where the void ratio wasdecreased by 17 vol %. When the composite base material having a voidratio of 40 vol % or more and less than 60 vol % was furtherheated/pressurized, the void ratio was most decreased at the fourthstage in one heating/pressurizing treatment, where the void ratio wasdecreased by 23 vol %.

The high-temperature composite base material obtained above wassubjected to a cooling/pressurizing step using a pair of cooling rollersat a temperature not more than the softening point of the thermoplasticresin. Then, a composite material plate having a thickness of 2.0 mm wasobtained. A test piece was cut out from the obtained composite materialplate and measured in accordance with JIS7164, as a result, the tensilemodulus ratio between an arbitrary direction and a direction orthogonalthereto was 1.05.

Incidentally, the average fiber length of carbon fibers in the obtainedcomposite base material or composite material was 20 mm that is thelength when the carbon fiber strand was cut. Similarly, the width of thecarbon fiber in the obtained composite base material or compositematerial was significantly narrower than 5 mm, and the thickness of thecarbon fiber was ½ or less of the width.

INDUSTRIAL APPLICABILITY

The composite base material of the present invention is suitable for theproduction of a carbon fiber-reinforced composite material useful forvarious applications such as automotive structural member.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope of the invention.

This application is based on Japanese Patent Application (PatentApplication No. 2012-151470) filed on Jul. 5, 2012, the contents ofwhich are incorporated herein by way of reference.

TABLE 1 Void Ratio of Composite Base Material (vol %) Tensile ModulusRatio First Second Third Fourth Fifth Sixth Seventh Occurrence of ofComposite Material Stage Stage Stage Stage Stage Stage Stage ProcessFailure (Eσ) Example 1 85 80 75 70 58 47 29 none 1.07 Example 2 83 78 6750 33 19 — none 1.12 Example 3 80 78 60 41 23 — — none 1.09 Comparative80 78 60 50 33 7 — none 1.43 Example 1 Reference goal: 67 — — — — — —occurred — Example 1 (unachieved) Reference 83 goal: 50 — — — — —occurred — Example 2 (unachieved) Example 4 59 59 38 38 8 — — none 1.18Example 5 69 69 53 53 30 20 — none 1.09 Example 6 74 74 62 62 43 16 —none 1.13 Example 7 79 79 68 68 53 21 — none 1.07 Example 8 75 75 63 6350 25 — none 1.04 Example 9 80 67 50 33 20 9 — none 1.08 Example 10 7260 43 20 10 — — none 1.05

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   1: Carbon fiber-   2: Pinch roller-   3: Rubber roller-   4: Rotary cutter main body-   5: Blade-   6: Cut carbon fiber-   7: Pitch of blades-   8: Blade parallel to fiber direction-   9: Heating/pressurizing roller-   10: Composite base material

The invention claimed is:
 1. A composite base material, comprising:carbon fibers having an average fiber length of 3 mm or more and 100 mmor less; and a thermoplastic resin is firmly fixed to the carbon fibersin an amount of 3 to 100 parts by mass with respect to 100 parts by massof the carbon fibers, wherein a void ratio of the composite basematerial is more than 7 vol % to less than 100 vol %, wherein a width ofthe carbon fibers is 5 mm or less and a thickness of the carbon fibersis ½ or less of the width, and wherein the carbon fibers are in amat-form material in which the carbon fibers are two-dimensionallyrandomly oriented and no carbon fibers are aligned in one direction on asurface thereof.
 2. The composite base material according to claim 1,wherein the composite base material is obtained by heating andpressurizing a mat-form material in which a carbon fiber mat and athermoplastic resin are combined, and the composite base material isobtained by applying heat and pressure so that a decrease in the voidratio does not exceed 40 vol % in one heating and pressurizingtreatment.
 3. The composite base material according to claim 1, whereinthe composite base material is obtained by heating and pressurizing amat-form material in which a carbon fiber mat and a thermoplastic resinare combined, and the composite base material has the void ratio of morethan 7 vol % to less than 80 vol %, obtained by preparing a compositebase material having a void ratio of 60 vol % or more and furtherheating and pressurizing the composite base material so that a decreasein the void ratio does not exceed 20 vol % in one heating andpressurizing treatment.
 4. The composite base material according toclaim 1, wherein the composite base material is obtained by heating andpressurizing a mat-form material in which a carbon fiber mat and athermoplastic resin are combined, and the composite base material is acomposite base material having a void ratio of from more than 7 vol % toless than 80 vol %, obtained by preparing a composite base materialhaving a void ratio of from 40 vol % to less than 60 vol % and furtherheating and pressurizing the composite base material so that a decreasein the void ratio does not exceed 30 vol % in one heating andpressurizing treatment.
 5. The composite base material according toclaim 1, wherein a carbon fiber bundle (A) constituted by the carbonfibers of not less than a critical number of single fibers, defined bythe following formula (1), is present in the carbon fibers:Critical number of single fibers=600/D  (1) wherein D is an averagefiber diameter (m) of single carbon fibers.
 6. The composite basematerial according to claim 5, wherein a ratio of the carbon fiberbundle (A) to a total amount of the carbon fibers contained in thecomposite base material is more than 0 vol % to less than 99 vol %. 7.The composite base material according to claim 5, wherein an averagenumber (N) of fibers in the carbon fiber bundle (A) satisfies thefollowing formula (2):0.7×10⁴ /D ² <N<2×10⁵ /D ²  (2) wherein D is the average fiber diameter(μm) of single carbon fibers.
 8. The composite base material accordingto claim 1, wherein the void ratio is more than 7 vol % to less than 90vol %.
 9. The composite base material according to claim 1, wherein thevoid ratio is more than 7 vol % to less than 40 vol %.
 10. The compositebase material according to claim 1, which is a long plate-shapedmaterial.
 11. A composite material obtained by pressurizing thecomposite base material according to claim
 1. 12. The composite materialaccording to claim 11, wherein a void ratio of the composite material isfrom 0 to 7 vol %.